The advantages and desirability of integrated optical devices is generally recognized, though their development is still in its early stages. The practical application of such integrated optics devices depends to a large extent on devising convenient methods for producing single mode channel waveguides which confine a beam of light energy in two dimensions. One major problem in the fabrication of such general optical waveguides arises from the extremely small size of the channel optical waveguide and also its very stringent dimensional tolerance. For example, the width of a single mode optical channel waveguide must generally be of the order of a wavelength of the light energy to be propagated and the wall roughness of the optical waveguide must generally be less than the order of one-tenth of a wavelength of such light energy in order to satisfactorily minimize light losses.
A number of prior art methods have been employed to produce such channel optical waveguides. For example, ion bombardment of fuzed quartz is one of the earliest methods for producing two dimension confinement of light energy within a material. This type of prior art technique was disclosed by E. R. Schineller, R. P. Flam, and D. W. Wilmet in Volume 58 of the Journal of the Optical Society of America at page 1171.
A more recent technique involving ion implantation in semiconductors was disclosed by E. Garmire, H. Stoll, A. Yariv, and R. G. Humperger in Volume 21 of Applied Physics Letters at page 28.
Another prior art method of fabricating such channel optical waveguides involved grooves which were embossed in a plastic material with the aid of a wire. The grooves were filled with polymethylmethacrylate which was later polymerized. This process forms polymeric channel waveguides as disclosed by R. Ulrich, H. P. Weber, E. A. Chandress, W. J. Tomlinson and E. A. Franke in Volume 20 of Applied Physics Letters at page 213.
Photolithographic techniques were also employed in the prior art to fabricate optical waveguide structures in semiconductors as reported by H. F. Taylor, W. E. Martin, D. B. Hall and V. N. Smiley in Volume 21 of Applied Physics Letters at page 95 and also by W. E. Martin and D. B. Hall in Volume 21 of Applied Physics Letters at page 325. In the employment of such prior art techniques, changes in the refractive index n of the waveguide are achieved by a diffusion process. Stated in its most simple context, for example, the index of refraction n of ZnSe may be increased by diffusing CdSe into it, since the index of refraction of ZnSe is less than the index of refraction of CdSe. Desirably this prior art method produces channel optical waveguides which exhibit relatively low-loss characteristics.
Another prior technique involves electro chemically induced migration of ions into glass to fabricate channel optical waveguides as disclosed and reported by T. Izawa and H. Makagome in Volume 21 of Applied Physics Letters on page 584.
Even more recently a prior art method of fabricating low-loss channel optical waveguides has been devised employing the technique of "photo locking" as disclosed and reported by E. A. Chandress, C. A. Pryde, W. J. Tomlinson, and H. P. Weber in Volume 24 of Applied Physics Letters at page 72. In the employment of this latter technique, channel optical waveguides four microns wide were produced by writing with the 364 nanometer line of a continuous-wave, argon ion laser on a polymer film having a methylmethacrylate base and doped with two-(1-mapthythl) acylate. The laser exposure selectively increases the index of refraction of the doped polymer. A photochemical reaction links the dopant to the polymer and also contributes to dopant dimerization and related chemical reactions. The films are then annealed by heating, which also removes the dopant in the unexposed parts of the film.
Accordingly, though considerable success has been achieved in developing methods for the fabrication of single mode low-loss channel optical waveguides, it is highly desirable that improved methods involving simpler processes be devised which will produce extremely narrow width channel optical waveguides with a high degree of accuracy and minimizing wall roughness of the optical waveguide to enhance its low-loss character.